1. Field of the Invention
The present invention relates to microactuators, methods for making the same, and magnetic head units and magnetic recording apparatuses using the same. In particular, the present invention relates to a method for making a microactuator which is assembled in magnetic head units and is suitable for precise alignment of the position of the magnetic head.
2. Description of the Related Art
A magnetic recording apparatus generally has a magnetic recording medium having a data-recording surface, such as a magnetic disk, a magnetic head for writing information into and reading the information from the magnetic recording medium, a head holder including a slider and a gimbal for supporting the magnetic head, and a head driver such as a voice coil motor for driving the head holder in order to align the position of the magnetic head with respect to a required track on the magnetic recording medium. In the alignment of the position of the magnetic head by the voice coil motor, current voice coil motors reach the limits of the alignment precision in consideration of a trend towards a finer track width. Thus, a proposed method is a combination of coarse adjustment of the head position using the voice coil motor and then fine alignment using a high-precision actuator.
FIGS. 7 and 8 show an example of a conventional actuator having high precision and capable of being finely movable. The actuator 101 shown in FIGS. 7 and 8 is generally called an electrostatic actuator which is driven by an electrostatic attractive force. The electrostatic actuator 101 includes two glass substrates, i.e., a first substrate 102 and a second substrate 103, facing each other with a given distance and movable with respect to each other in the horizontal direction. The first substrate 102 has a first comb electrode 104 having a plurality of comb elements 104a which are parallel to each other on an inner face 102a thereof, whereas, the second substrate 103 has a second comb electrode 105 having a plurality of comb elements 105a which are parallel to each other on an inner face 103a thereof. The comb elements 104a and the comb elements 105a are alternately arranged.
When a voltage is applied between the first electrode 104 and the second electrode 105 in the above electrostatic actuator 101, the comb elements 104a of the first electrode 104 and the comb elements 105a of the second electrode 105 are deeply engaged with each other by the electrostatic attractive force generated between the first electrode 104 and the second electrode 105. Thus, the first electrode 104 approaches the second electrode 105 so that the first substrate 102 and the second substrate 103 move with respect to each other. When the voltage is cut, the engagement is released due to the removal of the electrostatic attractive force. Thus, the first electrode 104 withdraws from the second electrode 105 so that the first substrate 102 and the second substrate 103 move with respect to each other in the reverse direction.
A conventional manufacturing process of the above electrostatic actuator 101 will be described with reference to FIGS. 9A to 9H. Referring to FIG. 9A, a resist film 201 having a predetermined pattern is formed on the upper surface and a resist film 202 is formed on the entire lower surface of a conductive silicon wafer 200. The conductive silicon wafer 200 is etched through the resist film 201 as a first mask, and then the resist films 201 and 202 are removed. A silicon wafer 200B having an outer shape shown in FIG. 9B is prepared. A resist film 203 is formed on the entire upper surface of the silicon wafer 200B and a resist film 204 having a predetermined pattern is formed on the lower surface of the silicon wafer 200B, as shown in FIG. 9C. The silicon wafer 200B is etched through the resist film 204 as a second mask, and then the resist films 203 and 204 are removed. A silicon wafer 200C having predetermined patterns on the two surfaces thereof is thereby prepared, as shown in FIG. 9D.
With reference to FIG. 9E, the silicon wafer 200C is bonded to a second glass substrate 103 provided with a predetermined wiring pattern (not shown in the drawing) of a metal such as aluminium, which is preliminarily formed using a third mask (not shown in the drawing), by an anodic bonding process to form a semi-finished product. A resist film 205 having a predetermined pattern is formed on the upper face of the silicon wafer 200C, as shown in FIG. 9F, and the silicon wafer 200C is etched through the resist film 205 as a fourth mask until the silicon wafer 200C is completely removed at unmasked regions. The resist mask 205 is removed to form electrode precursors 105B for the second electrodes on the second substrate 103 and electrode precursors 104B for the first electrodes, as shown in FIG. 9G, in which the electrode precursors 105B are connected to the electrode precursors 104B in the boundary regions (not shown in the drawing).
With reference to FIG. 9H, the electrode precursors 104B are bonded to a first glass substrate 102 having a predetermined wiring pattern of a metal such as aluminium, which is preliminarily formed using a fifth mask (not shown in the drawing), by an anodic bonding process to form the microactuator shown in FIGS. 7 and 8.
As described above, this manufacturing process needs five masks. A reduction in the number of masks and steps in this process would produce actuators with further reduced manufacturing costs.
Accordingly, it is an object of the present invention to provide a microactuator capable of reducing the number of masks in the production process and simplifying the production process, and a method for making the microactuator.
It is another object of the present invention to provide a magnetic head unit and a magnetic recording apparatus using the microactuator.
A microactuator in accordance with the present invention comprises a first substrate, a second substrate, the first substrate and the second substrate facing each other with a distance and movable with respect to each other, a first comb electrode having a plurality of first comb elements formed on an inner surface of the first substrate, a second comb electrode having a plurality of second comb elements formed on an inner surface of the second substrate, the first comb elements and the second comb elements being alternately disposed, and a connecting film formed by partially removing an interlayer formed on the inner face of any one of the first substrate and the second substrate, any one of the first electrode and the second electrode being bonded to the connecting film.
A method for making a microactuator in accordance with the present invention comprises providing a first substrate and a second substrate facing each other with a distance and movable with respect to each other, and providing a first comb electrode having a plurality of first comb elements formed on an inner surface of the first substrate and a second comb electrode having a plurality of second comb elements formed on an inner surface of the second substrate, wherein a wafer comprising two substrate layers and an interlayer provided therebetween is used as any one of the first substrate and the second substrate and one of the two substrate layers is etched using a mask having a predetermined pattern to form a first electrode precursor group and a second electrode precursor group for the first electrodes and the second electrodes, respectively, the interlayer below any one of the first and second electrode precursor groups is removed by etching to form any unconnected one of the first and second electrodes and to form the other one of the first and second electrodes supported by connecting films formed by etching of the remaining interlayer, and said unconnected one is bonded to the other one of the first substrate and the second substrate.
In the microactuator and the method for making the same in accordance with the present invention, either the first electrode or the second electrode is bonded to one of the first and second substrates via the connecting film. Thus, only the unbonded electrode is bonded to the other substrate not provided with the connecting film. That is, the bonding between the electrode and the substrate, which precludes precise alignment, can be achieved by only one bonding step. In contrast, the above conventional process requires two bonding steps. As a result, the method in accordance with the present invention facilitates precise alignment, improves the yield, and simplifies the production process.
The interlayer may be etched by a wet etching process using an etchant or a dry etching process using plasma etc. When one of the two substrate layers is etched through a mask having a given pattern to form the electrode precursors for the first and second electrodes, the dry etching process capable of vertically etching side walls is preferred.
The other substrate may comprise any insulating materials. In particular, glass which facilitates bonding is preferred.
In the microactuator in accordance with the present invention, the first electrode or the second electrode is bonded to the connecting film formed by partial etching of the interlayer. Thus, the gap formed between the electrode not bonded to the connecting film and the other substrate material can be uniformly and securely controlled to a predetermined value. When the gap is a fine gap on the order of less than 10 xcexcm, for example, several micrometers, the first electrode or the second electrode is not bonded to the other substrate in unrequited portions. As a result, the microactuator can be miniaturized.
In the microactuator, the first and second electrodes may comprise silicon and the interlayer may comprise a material which is selectively etched with respect to the silicon.
In the method for making the microactuator, one of the two substrate material layers may comprise silicon and the interlayer may comprise a material which is selectively etched with respect to the silicon.
Such a microactuator can be readily produced by using a wafer comprising two substrate layers and an interlayer disposed therebetween, by etching one of the two substrate layers to form the first and second electrodes, by etching the interlayer using the first and second electrodes as masks to form the first and second electrodes which are supported by the connecting film composed of the remaining interlayer and the other substrate layer.
The microactuator can be produced using only two masks, that is, a mask for forming a predetermined pattern onto one substrate layer of the wafer and another mask for forming electrodes supported by the connecting film.
In this microactuator, the first electrode, the second electrode, and the substrate provided with the connecting film may comprise silicon, and the interlayer may comprise at least one of the silicon oxide film and the silicon-boron-oxygen insulating film.
In the method for making the microactuator, both the substrate layers may comprise silicon and the interlayer may comprise at least one of the silicon oxide film and the silicon-boron-oxygen insulating film.
High bonding strength is secured between silicon and the silicon oxide film and between the silicon and the silicon-boron-oxygen insulating film. Thus, in the microactuator, high bonding strength is secured between the substrate and the connecting film formed by etching of the interlayer and between the connecting film and the first and second electrodes.
In the above microactuator, the first and second electrodes are readily formed by using a wafer comprising two silicon substrate layers and an interlayer and by etching the silicon substrate layers.
Since the electrode not bonded to the connecting film comprises silicon, this electrode can readily be bonded to a glass substrate by an anodic bonding process.
In the microactuator of the present invention, the first and second electrodes may comprise silicon, the substrate provided with the connecting film may comprise glass or ceramic, and the interlayer may comprise a polyimide.
In the method for making the microactuator, one of the substrate layers may comprise silicon, the other substrate may comprise glass or ceramic, and the interlayer may comprise a polyimide.
The polyimide interlayer is formed by coating a polyimide solution onto a glass or ceramic substrate by a spin coating process. Next, a silicon substrate is bonded to the intermediate layer by pressure to form a wafer having a triple-layer structure.
A resist is applied onto the wafer, the silicon substrate is etched by a photolithographic process to form the first and second electrodes, the polyimide interlayer is etched through the first and second electrodes as masks by an oxygen plasma process to form the first and second electrodes supported by the connecting film of the interlayer provided on the glass or ceramic substrate layer, and then the electrode not supported by the connecting film of the first and second electrodes is bonded to the other substrate opposing to the glass or ceramic substrate provided with the connecting film.
The magnetic head unit in accordance with the present invention has the above microactuator. In this magnetic head unit, positioning or tracking of the magnetic head at a required track on a magnetic disk is performed by the operation of a voice coil motor and precise alignment of the magnetic head is performed by the operation of an electrostatic actuator mounted at the tip of a gimbal. The accuracy of the tracking in the hard disk is thereby further improved and the magnetic head unit is highly reliable.